What is inside SIM Card (Subscriber Identity Module) ?

The SIM as mentioned previously is a “smart card” which plugs into the ME and contains information about the MS subscriber hence the name Subscriber Identity Module.

The SIM contains several pieces of information:

International Mobile Subscriber Identity (IMSI)This number identifies the MS subscriber. It is only transmitted over the air during initialization.

Temporary Mobile Subscriber Identity (TMSI)This number identifies the subscriber, it is periodically changed by the system management to protect the subscriber from being identified by someone attempting to monitor the radio interface.

Location Area Identity (LAI)Identifies the current location of the subscriber.

Subscriber Authentication Key (Ki)This is used to authenticate the SIM card.

Mobile Station International Services Digital Network (MSISDN)This is the telephone number of the mobile subscriber. It is comprised of a country code, a network code and a subscriber number.

Most of the data contained within the SIM is protected against reading (Ki) or alterations (IMSI). Some of the parameters (LAI) will be continuously updated to reflect the current location of the subscriber.

The SIM card, and the high degree of inbuilt system security, provide protection of the subscriber’s information and protection of networks against fraudulent access. SIM cards are designed to be difficult to duplicate. The SIM can be protected by use of Personal Identity Number (PIN) password, similar to bank/credit charge cards, to prevent unauthorized use of the card.

The SIM is capable of storing additional information such as accumulated call charges.

This information will be accessible to the customer via handset/keyboard key entry. The SIM also executes the Authentication Algorithm.